Understanding Java Objects: Classes, Methods, and Data Structures

1. You should understand everything on this slide publicclassTestClass { publicstaticvoid main(String[] args) { System.out.println("public static void main(String[] args) is where it all begins!"); intmyIntegerVariable = 77; System.out.println("I can have cool integer variables like " + myIntegerVariable); TestClassmyObject = newTestClass(); // I can also call functions like this myObject.myFunction("Test"); // ...but I haven't fully explained yet what the deal with "new" is // and how myObject is involved. } publicvoidmyFunction(String foo) { int[] arrayVariable = newint[25]; for(int i = 0; i < arrayVariable.length; i++) { System.out.println("Array Value at index " + i + " is " + arrayVariable[i]); } } }

2. Classes and ObjectsArrayListsHashMapsHashSets When arrays are just not cool enough.

3. In case you missed the email… • The Link is now staffed 5pm-11pm, Sunday-Thursday! Get help! • You first APT assignment is due tomorrow at 8am. How many folks are planning to be at the Link tonight? • Hangman (due next Wednesday 1/25 at 8am) is posted and ready to go. Many other things are coming due too! • Videos and notes will be linked off the syllabus

4. In the Optional Textbook • Read chapters 1-3 (should be fast, but do some of the exercises at the end of Chapter 3) • The later part of this class will also deal with bits of chapter 16

5. The Story Thus Far publicclassTestClass { publicstaticvoid main(String[] args) { System.out.println("public static void main(String[] args) is where it all begins!"); intmyIntegerVariable = 77; System.out.println("I can have cool integer variables like " + myIntegerVariable); TestClassmyObject = newTestClass(); // I can also call functions like this myObject.myFunction("Test"); // ...but I haven't fully explained yet what the deal with "new" is // and how myObject is involved. } publicvoidmyFunction(String foo) { int[] arrayVariable = newint[25]; for(int i = 0; i < arrayVariable.length; i++) { System.out.println("Array Value at index " + i + " is " + arrayVariable[i]); } } }

6. Objects: they combine data and functions together Data: “cgga” Functions: setStrandData getStrandData mutate addBasePair Data: “gattac” Functions: setStrandData getStrandData mutate addBasePair

7. addBasePair function DnaStrand strand = new DnaStrand(); strand.setStrandData(“cga”); //prints cga System.out.println(strand.getStrandData()); strand.addBasePair(“t”); //prints cgat System.out.println(strand.getStrandData());

8. Why Objects? • See the coolness of java’s String class!

9. BEWARE! Never compare 2 strings like this: String foo; String bar; //some other code if(foo == bar) { System.out.println(“Strings are equal!”) } Always compare them like this: if(foo.equals(bar)) { System.out.println(“Strings are equal!”) }

10. is3rdBasePairCytosine DnaStrand strand = new DnaStrand(); strand.setStrandData(“tac”); if(strand.is3rdBasePairCytosine()); { System.out.println(“cytosine!”); } The function is3rdBasePairCytosine returns a boolean – a primitive type that is either true or false You might check out the String Javadoc for some useful functions

11. 4 Classes You Will Get to Know is CompSci 100 • String • ArrayList – an expandable list you can add or remove elements from • HashSet – a list that prevents duplicate elements • HashMap – a “dictionary” where you can associate a particular key with a particular value

12. getBaseCounts public HashMap<Character,Integer> getBaseCounts() { HashMap<Character,Integer> baseCounts = new HashMap<Character,Integer>(); baseCounts.put(‘c’, 0); baseCounts.put(‘g’, 0); baseCounts.put(‘a’, 0); baseCounts.put(‘t’, 0); for(inti = 0; i < myData.length(); i++) { char currentBase = myData.charAt(i); //your code goes here } return baseCounts; } When you’re finished, submit your code via ambient.

13. What you should know • What the difference between class and objects is, and how objects work • 4 key java objects to help you with apts and homeworks: • String • ArrayList • HashMap • HashSet